1. Field of the Invention
This invention relates to a circuit breaker for the protection of lines against thermal overload and short circuits.
2. Description of the Prior Art
Such circuit breakers usually comprise terminals, contacting and quenching means, and a latching mechanism, which is adapted to be electromagnetically and thermoelectrically unlatched to open movable contacts in response to an overload. As has been mentioned, e.g., in EP 0 144 799, it is essential to provide a high switching capacity within a small overall size. A high switching capacity requires that the arc-quenching means are as large as possible.
Whereas EP 0 144 799 provides for that purpose a compact latching mechanism, it provides for the thermal and magnetic release a system which requires improvement as regards the simplification of its functional concept and a highly mechanized manufacture. This is particularly applicable to the number of parts and the number of welded joints required along the line.
Besides, circuit breakers are required to have a high short circuit breaking capacity and experience has shown that this imposes a high stress on conventional bimetal trips and shortens the useful life. In addition, such circuit breakers are manufactured in large numbers as they are required on any small distribution board and are permitted to have only a small power consumption themselves.
There is also a desire for a further decrease of the structural expenditure and for a further kinematic simplification, particularly as regards the spatial separation of important functional groups, on the one hand, and the possibility to provide a circuit breaker having a higher switching power within the conventional overall size.
DE 36 37 275 discloses for electric protective switching devices an overcurrent trip, in which protective functions consisting of the protection against a short circuit and a protection against a thermal overload are combined in one unit and in which the thermal trip does not carry current and which has a much lower power consumption (power loss) than the known designs. In that previously known overcurrent trip a thermal release is effected by a snap-action bimetal disk, which is mounted in a rotationally symmetrical carrying body that has a high thermal conductivity. But that printed publication does not disclose a combination of that overcurrent trip with a latching mechanism and arc-quenching means, as is required for high switching capacities.